1. Field of the Invention
The present invention relates to various kinds of processing apparatuses provided with a backpressure sensor.
2. Related Art
In order to carry out a processing operation in various kinds of processing apparatuses, it becomes necessary in some cases to detect the position and thickness of a workpiece in advance.
For example, a semiconductor chip utilized in various kinds of electronic devices is formed by dicing with use of a cutting apparatus a semiconductor wafer having a plurality of circuits formed on an outer surface thereof. It has been demanded to form a semiconductor chip thinner in order to reduce the dimensions and weight of an electronic device. In order to meet this demand, a technique called pre-dicing has been put to practical use.
The pre-dicing is a technique for forming in advance grooves in the depth corresponding to the thickness of a final semiconductor chip on an outer surface of a semiconductor wafer, thereafter exposing the groove on a rear surface of the semiconductor by grinding the rear surface of the semiconductor wafer, thereby dividing the resultant product into individual semiconductor chips. Therefore, in order to form a predetermined depth of grooves on an outer surface of a semiconductor wafer, it is necessary to know a vertical position of the outer surface of the semiconductor wafer prior to forming the grooves. When a cutting apparatus is used to form the grooves in the semiconductor wafer, it is known that a backpressure sensor is mounted on the cutting apparatus and a position of the outer surface of the semiconductor wafer is detected by using the backpressure sensor (refer to JP-A-2001-298003). The backpressure sensor disclosed therein is formed so that an air blowout nozzle is moved vertically by a driving mechanism including a pulse motor and a ball screw.
However, when a movement (downward movement) of the blowout nozzle does not stop and runs away due to trouble of the blowout nozzle, an air circulating pipe or a pressure measuring system, the blowout nozzle collides with the semiconductor wafer and damages the same. Such a problem is a problem occurring not only in a cutting apparatus but also in other processing apparatuses provided with a backpressure sensor and formed so that a blowout nozzle moves toward a workpiece.
In a processing apparatus provided with a backpressure sensor and formed so that a workpiece is detected by moving a blowout nozzle toward to the workpiece, a problem resides in the prevention of the collision of the blowout nozzle with the workpiece so as to avoid damage to the workpiece.